Ubuntu14.04安裝jdk1.8

//新建文件夾
sudo mkdir /usr/java

//解壓jdk
sudo tar zxvf jdk-8u25-linux-x64.tar.gz -C /usr/java

//添加環境變量
sudo gedit ~/.bashrc
//在文檔末尾添加如下代碼：
    export JAVA_HOME=/usr/java 
    export JRE_HOME=${JAVA_HOME}/jre  
    export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib  
    export PATH=${JAVA_HOME}/bin:$PATH 

//配置jdk版本
sudo update-alternatives --install /usr/bin/java java /usr/java/jdk1.8.0_25/bin/java 300  
sudo update-alternatives --install /usr/bin/javac javac /usr/java/jdk1.8.0_25/bin/javac 300  
sudo update-alternatives --install /usr/bin/jar jar /usr/java/jdk1.8.0_25/bin/jar 300   
sudo update-alternatives --install /usr/bin/javah javah /usr/java/jdk1.8.0_25/bin/javah 300   
sudo update-alternatives --install /usr/bin/javap javap /usr/java/jdk1.8.0_25/bin/javap 300 

sudo update-alternatives --config java
//若是初次安裝，則會提示沒有選項，否則會有選項可選

//測試
java -version
//會有如下輸出：
java version "1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode)